Method of retreading tires



Jan. 6, 1948. J. C.IHEINTZ 2,434,156 I METHOD OF RETREADING TIRES Filed June 6, 1945 2 Sheets$heet 1 w FIG. 3

INVENTOR.

JAMEJ C. HEM/r2.

Jan. 6, 1948. J, c. HEINTZ METHOD RETREADING TIRES Filed June 6, 1945 2 Sheets-Sheet 2 FIG. 8

M R 1/ Z 4 Z 24- xll RIM Z w M y M 2 A Patented Jan. 6, 1948 U N I T E D "S TATE S PATEN .F I'CiE *METIion-OF RE'rn-E'AniNG TIE-Es James C. Heintz, Lakewood;Ohio

Application June 6, 1945,'SerTal"No. "597,871

'4'Cia'ims. 1

This invention relates to an improved method of-retreading tires. More particularly, it relates to a new method 'of controlling the fit of a tire in a retreading mold so that the tire is retreaded without distortion. -It includes a template designed for use in carrying out the process.

According to this invention the buffed contour of the tire is measured from bead to bead before the application of the camelback used for retreading; and the tire is either buifed to a predetermined bead-to-bead measurement to fit a particular molding cavity, or if several molding cavities of different sizes are available, such as the graded sizes of molding cavities obtained by the use of interchangeable matrices and spacers in a. single mold, th correct cavity for retreading the tire is selected from the tires bufied measurement. A template may be used-to control the bufiingif desired.

In th -past the manufacturers of retreading equipment, generally speaking, havent given sufficient attention-to the necessity for retreading the tir in its natural shape. In fact, certain designers of retreading equipment anticipate the distortion of a tire to accommodateit to the type o'I" mold they hav 'designed. Some equipment requires the spreading of "the beads orfiattening of the tread; other equipment squeezes the tire in the mol'dingcavity. Therehas been no general recognition of the fact that instead of forcing th tire-to conform to the shape of a particularmol'd, a 'plurality of graded mold cavities should be provided, and the tire should be prepared for retreading in the cavity in which itcan be 'retread'ed with the least distortion and, preferably, Withoutany distortion.

According to this invention the selection of the best mold for retreading a tire and the control of the fit of the tire im 91, retreadin'g mold are conducted scientifically. The mold isselected n the basis of the bead-to-beadmeasurement or the tire to beretre'aded after bufli-n'g, and the tire may even'b buifed to the "exact contour of the tire that the mold is more particularlydesi'gned to retread. Th tire is buffed to a predetermined size to fit a particular molding cavity, or the proper molding "cavity is selected on the basis'of the contour of the landed tire. The cam'elbaek used must,'therefore, be of standard dimensions so that the space it will occupy can be determined in advance.

In carrying out my invention, 1 measure the buiTe'd tire from one bead,over the tire, to the other bead. If after the first bufiiirg the measurement is such that thetire must be "squeezed to nt into the available mold ca vity, the bufiiiig may be continued "until ae'ontour of the desired measurement is reached. S'uch bdifing may b'e done in conjunction with and controlled b'y a template which fi'ts the-buffed contour of the tir for "which the -r'r'16l'd was more particularly designed.

"The"recent tendency in the mantifaeture f'the carcass (if a tire -partic'iilarlya tire which is to be subjected to hig h temperature ofp'erations, such as an airplane-tire 'o'r atru'ck" or bus tireis to 'lrr'akethe carcass otasyrithetic fabr'ic. Rayon, nylon, --and the like have be'e'n'nsed extens'ive'ly. Thes synthetics lose less tensile strength than cotton-when su'bj'ected to riigh t'emperature'sfibut they stretch. Because they are "hdt ve'ry elastic, the tire gradually enlarges. i-his-enlargementis commonly called "-growt'h-."" It makes accurate measurementofthe tire prior to retreading "more necessary "than previously when 'tires did not grow sufficiently to appreciably change the tire size'throughuse andall tires of an original rated siz'e eould be retreaded in a mold designed for that rate'd siz'e.

I h'e need for accurate measurement of a tire as a, preliminary to 'retrea'ding is greatest in ai-rplane tires-and other tireswhich are entirely enelosed in the retrea'ding mold. Generally, in the retreading molds used for otter tires, such as passenger tires and triiek an'd bus 'tires,'the molding-caivit'y is confined to the tread and --s"houlde'1s and may include, also, a part of the side walls. However, the-Iower portion :or the side walls of such tires -is generally not enclosed in the retre'ading mold. sucn moles may be used with tires-mounted on rims I of Several di'fie'r'en't Widths because the lower por tiondf the side wall of the tire is hot confined *in the mold but may bulge more or less between the rim and the bottom of the outer mold I sui -fade.

Whether employed with an airplane tire or a different type (if tire, the-inethod'of 'masuri'ng and fitting he'reind'eSe'ribed. r'es'ults in better retreading than has heretofore been p'ossible because the tires are retreaded Without stretching or other distortion which --is necessar when the cavity in "which a tire ts to be retreaded i's selected by guess or has the result of less accurate measurement than here contem'plated.

In preparing a tire forretreading according to this-process, some oldru'bber is buffed off. lt is necessary to remov the shoulders and to give the tire a smoothly arched cross se'ctional con:- tour. "The contour-must be uniform throughout the Whole circumference of the tire. ts

3 readily obtained by mechanical bufiing. The buffing may advantageously be controlled by gauging the buffed contour with a suitable template. After buffing and before placing the new raw rubber stock (called camelback) in place, the outer contour of the tire is measured from the heel of one bead to the heel of the other bead. Th measurement is most advantageously made with a tape.

The bead-to-bead measurement of the tire is the important measurement in fitting the tire into the molding cavity. The rim diameter is kept constant by the metallic beads. There are numerous variables which should be considered. Any tire may be mounted on rims of difierent widths for retreading, and for each rim width a molding cavity of difierent size is required. A tire of shorter bead-to-bead measurement mounted on a wide rim may be cured in the same mold as a tire of longer bead-to-bead measurement mounted on a narrower rim. Different lug designs occupy different proportions of the volume of the molding cavity. In a mold without interchangeable parts the range of bead-to-bead measurements which can be accommodated for each rim width is easily calculated. Similar calculations may be made for molds with interchangeable matrices and spacers, each combination of any of the spacers with any of the matrices being particularly designed for a tire of a particular bead-to-bead measurement and buffed contour. The range of bead-to-bead measurements for each rim width for which each molding cavity is particularly designed should be calculated and tabulated for ready reference in carrying out this invention. Thereafter, when the bead-to-bead measurement of any tire becomes known, the mold and rim width suitable for retreading the tire, and also the particular spacer and matrices in molds provided with them are available at a glance.

The guesswork is thus eliminated. The tires are accurately fitted to the mold by selecting a mold cavity known to satisfactorily retread a tire mounted on a rim of a particular width and with a bead-to-bead measurement in the range of the measurement of the tire in question. The measurement is made before the application of the camelback.

Any particular mold cavity is designed more particularly for retreading a tire having a particular bufied contour. When a tire of this particular contour is retreaded in this mold, it is distorted less than a tire of any other contour. Due to the plasticity of the camelback some departure from the ideal is not serious. However, bumng to a particular contour for any selected mold cavity gives improved results. When a tire is to be buifed to a particular contour, as by testing with a template, it may be buffed till the bead- .to-bead measurement is about /2 inch greater than the range recommended for any mold before testing with the template. Then on subsequent bufling to fit the template, the bead-tobead measurement is brought within the range which the mold is designed to retread.

When a mold is equipped with a series of interchangeable matrices and spacers, the ranges of bead-to-bead measurements which adjacent members of the series will satisfactorily accommodate should. preferably overlap somewhat. The range of measurements which any particular combination may satisfactorily accommodate may vary 1 to 2 or 3 per cent each way from the calculated ideal. Less variation is possible 4 with molds which completely enclose a tire than with the other type of mold in which the side wall of the tire bulges more or less between the rim and the mold.

The invention will be further described in connection with the accompanying drawings, in which:

Fig. 1 illustrates schematically the method of measurement of a tire;

Fig. 2 is a cross section of an airplane tire in a retreading mold;

Fig. 3 is an enlarged view of the airplane tire shown in Fig. 2 with the matrices and adjustable rim shown on an enlarged scale;

Fig. 4 shows the same matrices used on a larger airplane tire with a spacer between the matrices and another in the rim;

Fig. 5 is a chart showing the variation provided by a series of spacers with a single matrix and the difierent sized airplane tires which can be thereby accommodated;

Fig. 6 is a cross section of a tire with ordinary straight side wallse. g., a passenger, bus or truck tire-with its tread and shoulders confined by matrices, the tire being mounted on a rim (partly broken away);

Fig. 7 is a cross section of a larger tire with a spacer between the matrices;

Fig. 8 is a chart showing the variation in a molding cavity which is provided by a single set of matrices using difierent spacers and rims of different widths; and

Fig. 9 illustrates the testing of a bufied tire with a template.

In Fig. 1 the tire i is shown in its bufied condition in full lines. The old shoulders 2, shown in dotted lines,must be buifed away before the tire is measured. The line with arrows 3 shows how the measurement is to be made from the heel of one bead to the heel of the other bead; but in measuring, the tape employed must be laid fiat against the buffed contour of the tire. Ordinarily, the contour of the tire is concave just above the bead. This may or may not be bridged, but all measurements should be made in the same manner. "The-tape must otherwise be laid fiat against the tire in order to secure an accurate measurement of the contour.

The illustrated full-circle mold, the cavity of which is variable by the insertion of interchangeable matrices and spacers, is of a wellknown type. It comprises annular steam chambers, such as the steam chambers in shown in Fig. 2. The annular matrices II and I2 together with the adjustable rim l3 completely enclose the airplane tire I5. The tire is shown in Figs. 2-4 as composed of the old tire I6 with the buffed contour I! shown in dotted lines and the new tread stock or camelback [8.

The camelback has a smooth contour and does not fill the mold until pressure is applied. When a steam bag or air bag I9 is inserted and inflated in the usual manner, it presses the camelback against the surface of the matrix so that the new tread takes the design of the matrices as illustrated in Figs. 2-4.

Fig. 3 shows the'matrices and rim without any spacer. As the matrices and rim completely enclose the tire in airplane-tire molds of the type illustrated, it is necessary to use spacers of the same size between the matrices and in the rim if any spacer is employed. The spacer between the matrices is indicated by the reference numeral 20 and the spacer in the rim by the reference numeral 2|. The width of the rim is a ents 8. readily adjusted by removing the nut 22 fromthe bolt which fits onto the head 23 and using a washer 24' or 25 or other suitable size, as re-' quired.

Fig. 5 shows how with a single set of matrices, known in the'trade as A1 57 0, the size of the mold cavity may be varied by using no spacer, or spacers of different widths. The table gives both the buffed dimension and the built-up dimension of the tire. The buffed dimension is the bead-to bead dimension discussed above. In the table under Buifed dimensions are three columns. The column headed Ideal gives the medium bead-toL-bea'd measurements for tires to be retreaded in the mold when equipped with a particular set of matrices and different spacers, as indicated. For example, with no spacer, a tire measuring 38% inches from the heel of one bead to the heel of the other bead fits nicely into the mold. The minimum and maximum dimensions given under the two other columns headed Buffed dimensions" show that some variation in beacl-to-bead measurement is possible without stretching or distorting the tire to any harmful extent. For example, with no'spacer, a tire with a bead-to-bead measurement of 38% to 39% inches may be retreaded. With a /2 inch spacer, a tire which measures a half inch more may be retreaded, as shown in the table. The increase in the size of the spacer increases the mold cavity, and as the bead-to-bead measurement increases, a larger mold cavity is required. It will be noted that using the same set of matrices and only the three spacers shown in the table, tires varying 2 /2 inches in bead-to-bead measurementnamel from 38% to 40% inches-may be retrea'ded without appreciable distortion or stretch- The stock size given in the table refers to the camelback which should be employed. There are four standard measurements for camelback for such tires. The first figure, M0, refers to the hump width of the stock. The hump widths vary by /8' inch. Hi indicates fourteen and no eighth inches hump width. I99 represents the base width. This, likewise, varies in" A inch. I90, therefore, represents a base width of 19 inches. The 14 refers to the thickness of the material in the center, and this is measured in thirty-seconds of an inch. The 14 represents W The 12 is the thickness of the stockat a point at the end of the hump width. This, likewise, is measured in thirty-seconds. Therefore, the camelback used with no spacer and with a /2 inch spacer meas ures 14 inches at the hump width, 19 inches at the base width, inch thick in the center, and inch thick at the end of the hump width. A different size of camelback is used with the wider spacers. The camelback measurements are standard.

To retread an airplane tire according to this invention, the tire is buiTed' to a smoothly arched contour, and the contour is then measured from the heel of one bead to the heel of the other bead. Assume, for example, that the bead-t0 bead measurement is 39 inches. Referring to the columns in the table of Fig. which give the buffed dimensions, we find that a tire measuring 39 inches may be vulcanized equally well in the mold without any spacer or with a /2 inch spacer. The spacer in the rim spreads the tire so that a, tire having a certain bead-to-bead measurement mounted on one rim may be retreaded in the same mold as a tire having a, longer or the 1% inch spacer.

6 shorter 'bead-"to'f-bead measurement if mounted on .a'narrower or wider rim.

Having selected the matrices and spacers (ii any) to be used, the mold is equipped, the camelback is stitched to the .bufied' surface after ce menting; etc'., as usual, and the tire with the camelback in place is provided with the steam" or air bag and mounted on the rim, the'retreading mold closed around it, and then the steam or air is turned into' the bag, and steam is turned into the steam chests of the mold to effect vul'canization in the usual manner.

Figs. 6 and 7 illustrate a mold equipped with matrices of the type generally employed for passenger, truck, and bus tires. It isnoted' that the tire is not entirely confined but that it is free between the bottom of the matrix 30 and the top of the rim 3i. This permits bulging which gives a little morefiexibility with this type of mold so that tires with a'somewh'at wider range of bead to-bead measurements can be satisfactorily re treaded in such equipment than where the matrix and rim come together as in the molds shownin Figs. 2-4.

Fig. 7 shows how a spacer 35 may be inserted between the matrices when used with a wider rim. But the rim width is not definitely tied to the size spacer employed because the fact that the side wall of the mold does not Contact the rim permits rims of different Widths to be used with no spacer and spacers" of different widths. This is more fully illustrated in the table of Fig. 8 where it is seen that such molds afford greater flexibility than is possible with molds of the type illustrated in Figs. 2-4.

The table of Fig. 8 relates to the retreadin'g of tires in molds such a those shown in Figs. 6' and '7, and is similar to the table of- Fig. 5 ex'-' cept that it shows the bead-to-bead dimensions of tires suitable for retreading with time of different widths. Using spacers of only two different widths and rims 1'1, 12 14, and 15 5 inches wide, respectively, as shown in thetable, a tire with a buffed b'ead-tO-bead dimension varying anywhere from 46 /2 inches (the mini-' mum for a 15 /2 inch rim) to 53 /2 inches (the maximum for an 11 inch rim) may be very satis factorily retreaded without substantial stretching' or distortion. The carnelb'ack employed for retreading in such molds is standard and is ofsuch size as to properly fill out the tread design, allowing for the usual un'dertread or rubber below the grooves in the tread design.

The process is illustrated by the following ex ample: Assume that an 18.00 x 24. tire is to' be retreaded' with the matrices shown. The tire is buffed to a smoothly arched contour and is measured' from the heel of one bead to the heel of another bead. Assume, for example, that the measured distance is 50 inches. The table shows that this tire, buffed to this dimension, may be satisfactorily retreaded using the 11 inch rim and inch spacer or using the same spacer with the 12 inch rim or using the 15 inch rim and Each of the three com binations will give a very satisfactory retrea'd. Gue'sswork is eliminated. The tire is actually measured and fitted to the exposed mold surface.

After deciding what rim width is most desired, cement, etc'., and standard camelback are applied to the buffed tire as usual, the mold is made ready with the designated matrices and spacer, the tire is equipped with a steam or air bag 32 and mounted on a rim of the size selected, and the tire is retreaded.

For the most accurate control, the tire is bufied to a bead-to-bead measurement just larger than that actually to be used. From this measurement the mold cavity best suited for retreading this tire i selected, bearing in mind the .fact that the bead-to-bead measurement is to be reduced about inch by further bufiing before the camelback is applied and the tire is put into the mold. Using a template with the contour of the tire for which this particular mold cavity was more particularly designed, the tire is then buifed to this template. As a check, the bead-to-bead measurement of the tire may be retaken after such further bufling to see that it falls within the intended range.

The template 40 of Fig. 9 is illustrative. It is provided with a marker 4| to indicate the center line of the tread and markers 42 to indicate the position of the shoulders. Such markers are desirable although not necessary. Using such a template, any tire 43 may be buffed to the exact contour of the tire the mold is more particularly designed to retread.

Although the drawings illustrate more particularly the application of the invention with a mold with interchangeable matrices and spacers, it is to be understood that the drawings and examples are illustrative. The invention is defined in the appended claims. In the claims reference to the use of a spacer refers to the use of a spacer of any width or no spacer at all.

What I claim is:

1. The process of retreading a tire, having available (a) a limited number of full-circle retreading molds of difierent tread contour, (b) a series of templates each cut to the contour of the buffed tire which each of the molds is particularly designed to retread, and (c) a chart giving the bead-to-bead measurements over the buffed contours of the tires which said molds are particularly designed to retread when mounted on rims of different widths; which process comprises (1) bufilng the tire to the general contour desired for retreading, (2) measuring the tire from bead to bead over the buffed contour, (3) on the basis of this measurement and with the aid of the chart selecting from the available molds that designed for retreading a tire with a bead-to-bead measurement over the buifed contour, which is just less than that of the measured contour of the tire to be retreaded and noting on the chart the rim width which gives such measurement, (4) buif ing the tire further so as to simultaneously (a) fit its buffed contour to that of the template cut to the contour of the buffed tire which the selected mold is particularly designed to retread and (b) reduce the buffed contour so that it more closely approximates that of the tire the selected mold is more particularly designed to re, tread, (5) mounting the buifed tire on the rim of noted width and applying camelback thereto, and then (6) curing the tire thus treaded in the selected mold.

2. The process of retreading a tire in a mold provided with a series of spacers of different width and adapted for retreading tires mounted on rims of different widths, using (a) a chart giving the measurements over the buffed contours from one head to the other bead Of the tire which the mold is more particularly designed to retread when used with each of the respective spacers of said series while mounted on rims of different widths and (b) a series of templates each having the contour of the buffed tire which the mold is more particularly designed to retread when used with each of the spacers; which process comprises (1) bufling the tire to give its tread the general contour of a tire which is to be retreaded, (2) measuring the tire over the buffed contour from one bead to the other bead, (3) from the chart selecting the spacer and rim width which gives a measurement over the bufied contour from bead to bead which is just less than the measured distance, (4) buffing the tire to the contour of the template which gives the contour of the buffed tire which the mold is more particularly designed .to retread when equipped with the selected spacer and thereby bringing the beadto-bead measurement of the bufied contour closer to that which the chart gives for the tire which the mold is more particularly designed to retread, (5) applying the camelback to the buffed surface and mounting the tire on the rim of determined wiclth, and then (6) curing the camelback while the tire is mounted on the rim.

3. The method of forming a new tread on a worn tire which comprises buffing the tire to a smoothly arched contour, measuring the bullied tire from bead to bead over said smooth contour before mounting on a rim, providing a molding cavity which is designed for use with a tire of somewhat smaller bead-to-bead measurement when uncured tread stock of standard dimensions is in place thereon and the tire is mounted on a rim of selected width, buffing old rubber from the outer surface of the tire to bring it to a beadto-bead measurement which is substantially the aforesaid smaller bead-to-bead measurement, placing uncured tread stock of standard dimensions in place on the buffed tire, and after mounting the tire on a rim of the selected width curing the tread stock to the tire in the molding cavity.

4. The method of forming a new tread on a worn tire which comprises buffing the tire to a smoothly arched contour, measuring the buffed tire from bead to head over said smooth contour before mounting on a rim, providing a molding cavity which is designed for use with a tire of somewhat smaller bead-to-bead measurement when uncured tread stock is placed thereon and the tire is mounted on a rim of selected width, selecting from a series of templates template with a contour which is the preferred contour for a tire with said desired bead-to-bead measurement, buffing old rubber from the outer sur face of the tire to bring it to a bead-to-bead meas. urement which is substantially the aforesaid smaller bead-to-bead measurement and cause it to fit the contour of the template, placing uncured tread stock of standard dimensions in place on the buffed tire and after mounting of the tire on a rim of the selected width curing the tread to the tire in the molding cavity.

JAMES C. HEINTZ.

REFERENCES CITED The following references are of record in the file of this patent:

UN ED S A S PA'I'E'NT Number Name Date 1,531,303 Miller Mar. 31, 1925 1,557,882 Schade Oct. 20, 1925 2,047,684 Heintz -1 July 14, 1936 2,202,683 Baesgen et a1. May 28, 1940 2,382,269 Stephens et a1 Aug. 14, 1945 

